1. Field of the Invention
This invention relates to N.sup.4 -acylcytosine arabinoside preparation having an enhanced activity as anti-tumor agents.
2. Description of the Prior Art
N.sup.4 -acylcytosine arabinoside is a derivative of cytosine arabinoside which is known as an agent for an acute leukemia, and it is particularly useful for anti-tumor agents having an improved durability of the activity and resistance to cytidine deaminase while it maintains a superior anti-tumor activity of cytosine arabinoside. (Cancer Research, Vol. 36, Page 2726 and Vol. 37, Page 2481)
The inventors of this invention have found that the anti-tumor activity of cytosine arabinoside is drastically enhanced by encapsulating cytosine arabinoside into liposomes comprising lipids such as sphingomyelin and lecithin. They have also found that an additive such as stearylamine and dicetyl phosphate was required to add cytosine arabinoside, since the amount of cytosine arabinoside encapsulated in liposomes is considerably small compared with that employed as the starting material. (Japanese Patent Application (OPI) 114015/1977) The above described additive, however, is harmful to living body. Therefore, it has been an important subject to increase the encapsulating efficiency of cytosine arabinoside into liposomes without using any harmful additive in this field.
The object of this invention is to provide a N.sup.4 -acylcytosine arabinoside preparations having an enhanced anti-tumor activity.
Another object of this invention is to provide an encapsulated N.sup.4 -acylcytosine arabinoside preparation without using any harmful additives.